HIGH-TEMPERATURE OXIDATION OF TI-48AL-2NB-2CR AND TI-25AL-10NB-3V-1MO

The short-term oxidation behavior of a gamma-TiAl alloy (Ti-48Al-2Nb-2 Cr) was compared and contrasted to that of an alpha(2)-Ti3Al base (Ti- 25Al-19Nb-3V-1Mo) alloy. Oxidation of Ti-25Al-10Nb-3V-1Mo was found to occur at a moderate rate at 800 degrees C, in a N-2+20% O-2 environme nt. A large increase in the oxidation rate occurred above this tempera ture. This large weight increase was attributed to a breakdown in the protective oxide scale on the surface of the aa intermetallic alloy, t hereby permitting rapid diffusion of oxygen and nitrogen to the surfac e of the intermetallic. The oxidation rate of this alloy at 1200 degre es C was not significantly higher than the oxidation rate at 1000 degr ees C. In contrast, the oxidation rate of Ti-48Al-2Nb-2Cr remained low up to 1200 degrees C. At this temperature, a significant increase in oxidation was observed and was attributed to accelerated oxygen diffus ion through the at phase and increased solubility of oxygen in the gam ma phase of the intermetallic microstructure. This weight increase occ urred despite the fact that at 1200 degrees C, the integrity of the ox ide layer formed on the surface of this alloy was maintained. The resu lts of this study illustrate the need for developing protective enviro nmental coatings tailored to the individual intermetallic alloy.